1. Field of the Invention
This invention relates to a light emitting diode module, more particularly to a light emitting diode module having improved heat dissipation efficiency and to a method for making the light emitting diode module.
2. Description of the Related Art
Light emitting diodes (LEDs) have properties of relatively long service life, low contamination, low power consumption, compact size, relatively fast reaction, etc. Thus, in recent years, an LED module formed by mounting the LEDs on a printed circuit board has been used for replacing a conventional light source.
When the current LED module is in use, only about 20 percent of the energy applied to the LED module is converted to light emanation, and about 80 percent of the energy is converted to heat energy. With the improving of the luminance and power of the LEDs, an issue concerning how to improve the heat dissipation efficiency of the LEDs becomes more and more important. If the LED module cannot dissipate the heat energy efficiently, a luminous decay of the LEDs would happen, thereby limiting the applications of the LED module.
Referring to FIG. 1, a conventional LED module with a heat dissipation structure for a display is disclosed in Taiwanese patent publication no. 200722840, and includes a back plate 10, a printed circuit board 11 and a LED package 13. The printed circuit board 11 is disposed on the back plate 10 and includes a circuit layer 111, a heat-resistant plastic layer 112, and a through hole 113 penetrating the circuit layer 111 and the heat-resistant plastic layer 112 and for extension of a protrusion 101 of the back plate 10. The LED package 13 includes a metal seat 131, an LED chip 132 and an insulative packaging member 133. The metal seat 131 has a lower surface 1311 aligned with the through hole 113 and connected with the protrusion 101 of the back plate 10. The LED chip 132 is attached to an upper surface of the metal seat 131 and is electrically connected to the circuit layer 111. The metal seat 131 is surrounded by the insulative packaging member 133. By disposing the LED chip 132 on the upper surface of the metal seat 131, the heat generated from the LED chip 132 can be conducted to the back plate 10 via the metal seat 131.
However, the provision of the metal seat 131 will increase the total thickness of the LED module. Moreover, after long-term use, the insulative packaging member 133 is likely to degrade or discolor to cause a luminous decay of the LED module and to damage the electrical connection between the LED chip 132 and the circuit layer 111, such that the lifetime of the LED module is shortened.
A planar light source device as shown in FIG. 2 has been proposed in U.S. patent application publication no. 2009-0242908 A1. The planar light source device includes a metal substrate 15, a printed circuit board 16 disposed on the metal substrate 15, and a plurality of LED chips 17 separately disposed on the printed circuit board 16. The planar light source device can provide relatively good heat-dissipation efficiency by modifying a thickness of the metal substrate 15 and by controlling areas of the LED chips 17 and the distance between any two adjacent ones of the LED chips 17. However, in this case, the thickness of the metal substrate 15 is required to be larger than 1 mm, and thus, the flexibility of the planar light source device is relatively poor. On the other hand, if the thickness of the metal substrate 15 is reduced, the heat generated by the LED chips 17 cannot be dissipated efficiently.